(i) Field of the Invention
(ii) Description of the Related Art
Since a cardiomyocyte loses a proliferative ability in an adult body, it is necessary to conduct cardiac transplantation in treating a serious heart disease such as cardiac infarction or cardiomyopathy. However, currently, since insufficient donor hearts are available, there is now a pressing need to develop a method of treatment other than cardiac transplantation. On the other hand, the recruitment of the ex vivo produced cardiomyocyte is expected to be a most promising method of providing relief for patients in need of cardiac transplantation.
Various methods of preparing a cardiomyocyte have been investigated, such as a method of using a differentiated embryonic stem cell, a method of inducing and differentiating a stem cell (somatic stem cell) isolated from a living body that is suggested to be within the body, and so on. However, there is a problem in the art that, it is in the nature of a stem cell that cells other than a cardiomyocyte are always developed from the stem cell as a by-product during the differentiation/induction procedure and that an undifferentiated stem cell always remains even after the differentiation/induction procedure. Thus, it has been considered in the art that the differentiated/induced cell population itself can not be used in the treatment method. Therefore, it is necessary to select a cardiomyocyte from the differentiated/induced cell population in order to successfully achieve cardiac transplantation in a human.
To date, an effective method of purifying a cardiomyocyte is not reported in the art other than a method of purifying a cardiomyocyte by incorporating in advance a marker gene into genome of the stem cell (FASEB J., 2000, 14: 2540-2548). However, since alteration of genome includes intrinsic ethical concerns and involves unpredictable serious risks including changes in the rate of malignant alteration, alteration of genome for practical use in a human raises significant questions.
It is known in the art that myocardial oxygen demand is relatively higher than that of major tissues other than heart and that the content of myocardial mitochondria is also relatively higher than that of other tissue (Am. J. Physiol., 1985, 248: R415-421). Further, it is well known in the art that a cardiomyocyte seriously loses mitotic capacity once the cell has differentiated and matured. However, it was not previously known at all that those ordinarily skilled in the art had tried to select a cardiomyocyte by applying the characteristics of the cardiomyocyte described above. Further, there was no report of directly comparing a mitochondrial transmembrane potential of the cardiomyocyte with mitochondrial transmembrane potential of other types of cells, of focusing on the mitochondrial transmembrane potential, and of selecting the cardiomyocyte using mitochondrial transmembrane potential as an indicator of the cardiomyocyte.
[non-patent document 1] FASEB J., 2000, 14: 2540-2548
[non-patent document 2] Am. J. Physiol., 1985, 248:R415-421